Optical transceiver with optical multiplexer on a flexible substrate

ABSTRACT

An optical transceiver for converting and coupling an information-containing electrical signal with an optical fiber including an optical fiber coiled over at least a portion of its length; a support element disposed in the transceiver module; a substrate for securing said coiled optical fiber to said support element to enable said coiled fiber to bend from a first direction to a second opposite direction inside said transceiver module; and an optical multiplexer secured to said substrate for receiving first and second optical fibers and multiplexing respective optical signals on said first and second optical fibers into a multi-wavelength beam onto a third optical fiber.

REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.10/879,775 filed Jun. 28, 2004, and assigned to the common assignee (nowU.S. Pat. No. 7,359,641, issued on Apr. 15, 2008).

This application is a divisional patent application of U.S. Ser. No.11/517,868 filed on Sep. 8, 2006, (now U.S. Pat. No. 7,578,624, issuedon Aug. 25, 2009), which is a divisional patent application of U.S. Ser.No. 11/266,152 filed on Nov. 3, 2005 (now U.S. Pat. No. 7,242,824,issued on Jul. 10, 2007), which is a divisional patent application ofU.S. Ser. No. 10/898,086 filed on Jul. 23, 2004 (now U.S. Pat. No.6,974,260, issued on Dec. 13, 2005).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to optical transceivers, and in particular tocoupling assemblies or modules that provide a communications interfacebetween a computer or communications unit having an electricalinput/output connector or interface and an optical fiber, such as usedin fiber optic communications links.

2. Description of the Related Art

A variety of optical transceivers are known in the art which include anoptical transmit portion that converts an electrical signal into amodulated light beam that is coupled to an optical fiber, and a receiveportion that receives an optical signal from an optical fiber andconverts it into an electrical signal. In a high-speed unit, opticaltransmitter subassemblies include several lasers operating at differentwavelengths and modulated with respective electrical signals foremitting a plurality of laser light beams. These beams are coupled intoa plurality of optical fibers, which converge in an optical multiplexerfor receiving the beams and multiplexing the respective optical signalsinto a single multi-wavelength beam that is coupled to a fiber opticconnector for transmitting the optical signal to an external opticalfiber.

SUMMARY OF THE INVENTION 1. Objects of the Invention

It is an object of the present to provide an improved opticaltransceiver using a flexible substrate to route and secure opticalfibers from a transmitter subassembly.

It is also an object of the present to provide an improved opticaltransceiver using a flexible substrate to route and secure opticalfibers from a subassembly.

It is another object of the present invention to provide a fusedbiconical tapered (FBT) coupler or similar multiplexing device mountedon a flexible substrate for use in a multi-laser optical transmissionsubassembly.

It is still another object of the present invention to provide anoptical transceiver for use in an optical transmission system with anindustry standard XENPAK housing and including a flexible substratetherein for routing optical fibers.

2. Features of the Invention

Briefly, and in general terms, the invention provides an opticaltransceiver for converting and coupling an information-containingelectrical signal with an optical fiber, including a housing andelectro-optical subassembly in the housing for converting between aninformation-containing electrical signal and a modulated optical signalcorresponding to the electrical signal from which at least two opticalfibers extend; and a flexible substrate for securing each of saidoptical fibers to prevent tangling or breakage during manufacturing andassembly and to enable said fibers to bend from a first orientation to asecond orientation.

In another aspect of the invention, there is provided an opticaltransceiver including an optical multiplexer mounted on a flexiblesubstrate for receiving at least first and second optical fibers andmultiplexing the respective optical signals on the optical fibers into asingle multi-wavelength beam in a single third optical fiber.

Additional objects, advantages, and novel features of the presentinvention will become apparent to those skilled in the art from thisdisclosure, including the following detailed description as well as bypractice of the invention. While the invention is described below withreference to preferred embodiments, it should be understood that theinvention is not limited thereto. Those of ordinary skill in the arthaving access to the teachings herein will recognize additionalapplications, modifications and embodiments in other fields, which arewithin the scope of the invention as disclosed and claimed herein andwith respect to which the invention could be of utility.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of this invention will be betterunderstood and more fully appreciated by reference to the followingdetailed description when considered in conjunction with theaccompanying drawings, wherein:

FIG. 1 is an exploded perspective view of an optical transceiver in anexemplary embodiment in accordance with some aspects of the presentinvention;

FIG. 2 is a top view of the flexible substrate for securing the opticalfibers; and

FIG. 3 is a rear view of the flexible substrate of FIG. 2.

FIG. 4 is a block diagram of an optical multiplexer according to oneexemplary embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Details of the present invention will now be described, includingexemplary aspects and embodiments thereof. Referring to the drawings andthe following description, like reference numbers are used to identifylike or functionally similar elements, and are intended to illustratemajor features of exemplary embodiments in a highly simplifieddiagrammatic manner. Moreover, the drawings are not intended to depictevery feature of actual embodiments or the relative dimensions of thedepicted elements, and are not drawn to scale.

Referring more particularly to FIG. 1, there is provided an opticaltransceiver 100 for operating over both multimode (MM) and single mode(SM) fiber using multiple laser light sources, multiple photodetectors,and an optical multiplexing and demultiplexing system. This enables asingle transceiver module to communicate over multiple protocols and atmaximum distance goals. The transceiver 100 and its housing 102 aredesigned such that maximum operating efficiency is achieved costeffectively and at reduced electromagnetic interference (EMI) andthermal levels in an industry standard form factor or package design.

Advantageously, the transceiver 100 is manufactured in a modular mannerpreferably using three separately mounted circuit boards mounted in thehousing—a transmitter subassembly, a receiver subassembly, and aprotocol processing board, with each board having dedicated functionsand electrically connected to each other using either flex circuitry,mating multipin connectors, land grid arrays, or other electricalinterconnect devices. This enables the basic transceiver module to beconfigured to different protocols and to support differentoptoelectronic devices using a simple subassembly configuration change,thus minimizing manufacturing costs and eliminating the need formanufacturing different transceivers for each different application. Inaddition, the use of flex circuitry or detachable connectors tointerconnect the boards allows for a modular interchangeable boarddesign (e.g., receiver, transmitter and PCS functionality each onseparate boards). Although the preferred design uses three boards, anytwo of the functions may be combined on a single board for an even morecompact design.

The modularity of the board design also enables the placement ofheat-sensitive components in the optimal location with respect to theheat-generating components (lasers and ICs) within the module housing102. It also makes it convenient and realistic to test and troubleshootseparate modular subassemblies independently before final assembly. Inaddition, the flex or other interconnects allow for manufacturing of thevarious boards (RX, TX, PCS) to proceed in parallel instead of inserial, hence reducing the manufacturing time for the entire unit.

Referring now to FIGS. 1, 2, and 3, an exemplary optical transceivermodule 100 is shown according to a preferred embodiment of the presentinvention. In this particular embodiment, the module 100 is compliantwith the IEEE 802.3ae 10GBASE-LX4 Physical Media Dependent sub-layer(PMD) standard and the XENPAK™ form factor. It is to be noted, however,that the transceiver module 100 may be configured to operate undervarious other compliant protocols (such a Fibre Channel or SONET) and bemanufactured in various alternate form factors such as X2. The module100 is preferably a 10 Gigabit Coarse Wavelength Division Multiplexed(CWDM) transceiver having four 3.125 Gbps distributed feedback lasersand provides 300 meter transmission over legacy installed multimodefiber and from 10 to 40 km over standard single mode fiber.

The transceiver module 100 includes a two-piece housing 102 with a base104 and a cover 106. In addition, contact strips 152 are provided toground the module to chassis ground as well. The housing 102 isconstructed of die-cast or milled metal, preferably die-cast zinc,although other materials also may be used, such as specialty plasticsand the like. Preferably, the particular material used in the housingconstruction assists in reducing EMI. Further EMI reduction may beachieved by using castellations (not shown) formed along the edges ofthe housing 102.

The front end of the housing 102 includes a faceplate 152 for securing apair of receptacles 124, 126. The receptacles 124, 126 are configured toreceive fiber optic connector plugs 128, 130. In the preferredembodiment, the connector receptacles 124, 126 are configured to receiveindustry standard SC duplex connectors (not shown). As such, keyingchannels 132 and 134 are provided to ensure that the SC connectors areinserted in their correct orientation. Further, as shown in theexemplary embodiment and discussed further herein, the connector plugreceptacle 130 receives an SC transmitting connector and the connectorplug 128 receives an SC receiver connector.

In particular, the housing 102 holds three circuit boards, including atransmit board 108, a receive board 110 and a physical coding sublayer(PCS)/physical medium attachment (PMA) board 112, which is used toprovide an electrical interface to external electrical systems (notshown). An optical multiplexer (MUX) 114 interfaces to the transmitboard 108 via an assembly of four distributed feedback (DFB) lasers 116in TO-cans. The lasers 116 are secured in place at the base 104 of thehousing 102 using a laser brace 118. The laser brace 118 also functionsas a heat sink for cooling the lasers 116. In addition, the transmitboard 108 and receive board 110 are connected to the PCS/PMA board 112by respective flex interconnect 120, or other board-to-board connectors.Thermally conductive gap pads 160 and 161 are provided to transmit theheat generated by the lasers or other components to the base 104 orcover 106 of the housing, which acts as a heat sink. The receiversubassembly 110 is directly mounted on the housing base 104 using athermally conductive adhesive to achieve heat dissipation. Differentsubassemblies therefore dissipate heat to different portions of thehousing for more uniform heat dissipation. As illustrated in FIGS. 1 and2, the output of the four lasers 116 is then input into the optical MUX114. The MUX 114 is mounted on a flexible substrate 140. The substrate140 may be an optical flexible planar material, such as FlexPlane™available from Molex, Inc. of Lisle, Ill., although other flexiblesubstrates may be used as well. As shown, the optical fibers 117 a, 117b, 117 c, 117 d originating from the laser assembly 116 and being inputinto the MUX 114 are mounted to the substrate 140. The output of the MUX114, which is routed to the transmit connector plug 130, is alsoattached to the substrate 140. The fibers 117 a, 117 b, 117 c, 117 d arerouted and attached in such a manner as to minimize sharp bends in theoptical fibers to avoid optical loss and mechanical failure.

The substrate 140 includes an opening 142 or hole in a portion of thematerial that is located directly above the retimer IC or other heatgenerating components mounted on the PCS/PMA board 112. The opening 142,which is substantially an area the size of the unused portion of thesubstrate 140, enables the heat sink on the cover to contact a heattransmission gap pad 160, so as to provide access to the mountedcomponents on the board. This area normally would be inaccessible if notfor the opening 142. For example, a heat sink may be installed in theClock and Data Recovery components (not shown) without interfering withthe routing of the optical fibers on the substrate 140 and withoutremoving the mounted substrate 140 to allow access to the PCS/PMA board112.

Several additional advantages are realized in using the flexiblesubstrate 140. In particular, attaching the fibers to the substrate 140,rather than allowing the fibers to move about freely within thetransceiver module housing 102, neatly maintains the routing of theoptical fibers to prevent unwanted tangling and breakage during assemblyof the transceiver. Furthermore, attaching the optical fibers to thesubstrate 140 greatly reduces the stress on the fibers, thereby reducingthe incidence of microcracks forming in the fiber coatings.

The present invention implements the transceiver 100 utilizing the fourstandard, commercially available fiber pigtailed lasers 116 whichinterface to a Fused Biconical Tapered (FBT) coupler 114 to collect andmultiplex laser radiation into a single fiber. Although an FBT ispreferred, an arrayed waveguide grating, multimode interference coupler,or combination of spatially fixed optical elements such a lens 114 a,optical interference filters 114 b, diffractive optical elements 114 c,dielectric or metallic mirrors 114 d, or other optical components, asshown in FIG. 4, may be used as well. The fiber that is used in thefiber pigtailed lasers 116 and the FBT 114 is affixed to the flexiblesubstrate material 140. This prevents fiber tangling and breakage whileremaining flexible and therefore easy to work with. The flexiblesubstrate material 140 may be an optical flexible planar material, suchas FlexPlane™ available from Molex, Inc, of Lisle, Ill., or Kapton™available from E. I. Dupont de Nemours and Company of Wilmington Del.Other flexible substrates may be used as well. A conforming coating isused over the entire flexible substrate 140 to secure the fibers to theflexible substrate 140.

As previously noted above, several additional advantages are realizedwhen using the flexible substrates 140 rather than allowing the fibersto move about freely within the transceiver module housing 102.Furthermore, attaching the optical fibers to the substrate 140 greatlyreduces the stress on the fibers, thereby reducing the incidence ofmicrocracks forming in the fibers. The fibers are routed and attached insuch a manner as to minimize sharp bends.

It will be understood that each of the elements described above, or twoor more together, also may find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in atransceiver for an optical communications network, it is not intended tobe limited to the details shown, since various modifications andstructural changes may be made without departing in any way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

1. An optical transceiver module for converting between an informationcontaining electrical signal and a modulated optical signal transportedover at least one optical fiber in the transceiver module comprising: atleast one optical fiber coiled over at least a portion of its length; aphysical support disposed in the transceiver module; a flexiblesubstrate for securing said at least one coiled optical fiber to saidsupport to enable said coiled fiber to bend from a first direction to asecond opposite direction inside said transceiver module, wherein thecoiled optical fiber provides a continuous optical path between thefirst direction and the second opposite direction; and an opticalmultiplexer mounted on said flexible substrate for receiving first andsecond optical fibers and multiplexing respective optical signals onsaid first and second optical fibers into a single multi-wavelength beamonto a single third optical fiber, wherein said optical multiplexer isselected from the group consisting of an arrayed waveguide grating and amultimode interference coupler.
 2. An optical transceiver as defined inclaim 1, further comprising: a housing having a cover and a base; anoptical receive board directly mounted to the housing base; and a fiberoptic connector receptacle in the housing that couples an opticalcommunications signal from an external optical fiber to the receiveboard.
 3. An optical transceiver as defined in claim 2, furthercomprising an electro-optical subassembly including a plurality oflasers for converting between said information-containing electricalsignal and said modulated optical signal corresponding to the electricalsignal from which at least two optical fibers engage said flexiblesubstrate to prevent tangling.
 4. A transceiver as defined in claim 1,wherein said flexible substrate comprises a Kapton™ film.
 5. Atransceiver as defined in claim 1, wherein said flexible substratecomprises a FlexPlane™ material.
 6. An optical transceiver as defined inclaim 1, further comprising a conforming coating over the flexiblesubstrate to secure said at least one coiled optical fiber.
 7. Atransceiver as defined in claim 1, further comprising an electro-opticalsubassembly including first and second lasers operating at differentwavelengths and modulated with respective first and second electricalsignals for emitting first and second laser light beams coupled to saidfirst and second optical fibers, respectively.
 8. A transceiver asdefined in claim 1, wherein said single third optical fiber is securedto said flexible substrate.